This invention relates to a cable assembly for actuating and releasing a parking brake and means whereby a release spring that acts on an end of a cable engages a flange on a backing plate of to limit the force of the release spring and prevent the release spring from moving the first and second brake shoes out of radial alignment with a backing plate and into axial engagement with a drum.
A parking brake is often associated with a drum brake and activated by a cable moving a lever to mechanically move first and second brake shoes into engagement with a drum to effect a parking brake application. Numerous mechanisms have been devised for attaching the cable to the end of the lever such as the ball retention structure as disclosed in U.S. Pat. No. 5,142,935 and the resiliently positioned bushings as disclosed in U.S. Pat. Nos. 5,105,682 and 5,174,170. These type connections function in an adequate manner with respect to a drum brake but with the introduction of drum-in-hat structure associated with four wheel disc brakes, the space available for the inclusion of parking brake components was limited and as a result new actuation devices were developed such the lever disclosed in U.S. Pat. No. 5,180,037 and the cross pull structure disclosed in U.S. Pat. No. 6,234,281. In a cross pull actuation device, a release spring is fixed to the knuckle of a suspension system. On termination of an input force applied through a cable to effect a parking brake application, the release spring moves the cable and allows the actuator mechanism to be moved to a position of rest by springs associated with the first and second brake shoes that also move the brake shoes out of engagement with an engagement surface on the drum. Unfortunately, the force on the release spring may at times also act on the actuator mechanism and move the first and second brake shoes out of radial alignment with the backing plate and into axial engagement with the drum such that noise is produced and damage may occur to the first and second brake shoes.
A primary object of the present invention is to provide a drum-in-hat brake with structure with means such that on the termination of an input force applied to a cable for effecting a parking brake application, the release force of a release spring is limited and as a result a radial alignment between first and second brake shoes and a backing plate is not changed by the release spring acting on and moving an actuator mechanism and first and second brake shoes with respect to a backing plate for the parking brake.
In more particular detail, the drum-in-hat park brake for a vehicle according to the present invention has first and second brake shoes that are positioned on and radially aligned on a backing plate by first and second pins secured to a backing plate that is fixed to a knuckle of a suspension system in a vehicle. Each of the first and second brake shoes has a first end that is aligned with respect to an anchor post extending from the knuckle and selectively spaced apart from each other by an actuator mechanism while a second end for the first and second brake shoes are linked to each other by an adjuster mechanism. A resilient arrangement including at least first and second return springs is attached to the first and second brake shoes for urging the first ends toward the anchor and the second ends toward the adjuster mechanism to define a rest position for the first and second brake shoes. In the rest position, a running clearance is established between the first and second brake shoes and an engagement surface on the drum. A cable assembly that is fixed to the knuckle has a first end that is connected to a lever of the actuator mechanism and a second end that receives an input force from an operator. The cable assembly responds to an input force applied to the second end by pulling on the lever to expand the actuator assembly and move the first and second brake shoes from the position of rest into engagement with a drum to effect a parking brake application. On termination of the input force on the second end, a release spring in the cable assembly urges the first end toward the actuator mechanism to allow the resilient arrangement to move the first and second brake shoes to the position of rest. The backing plate is characterized by a flange with a horizontal slot therein that is aligned with the lever of the actuator mechanism while the cable assembly is characterized in that the first end includes a stem with an annular rib thereon. The stem passes through the horizontal slot and is connected with the lever while the annular rib engages the flange to limit the movement of the first end toward the actuator mechanism by the release force applied by the release spring on the cable. Thus, the stem does not move the lever in the actuator mechanism past a position of rest nor push on the lever to change the radial alignment between the first and second brake shoes with respect to the backing plate on termination of the input force.
An advantage of the cable assembly and backing plate connection provided by the present invention resides in the limiting action of the release spring in moving the actuator mechanism to a position of rest without effecting a radial alignment between the brake shoes and backing plate.
An object of this invention is to provide structure whereby a release spring of a cable assembly is caged between a backing plate and a knuckle to prevent the force of the release spring from effecting the radial alignment between brake shoes and a backing plate in a drum-in-hat brake.